distance_recorder<DistanceMap, EventTag>

This is an EventVisitor that records
the distance of a vertex (using a property map) from some
source vertex during a graph search. When applied to edge e =
(u,v), the distance of v is recorded to be one more than
the distance of u. The distance recorder is typically used with
the on_tree_edge or on_relax_edge events, and
cannot be used with vertex events.

distance_recorder can be used with graph algorithms by
wrapping it with the algorithm specific adaptor, such as bfs_visitor and dfs_visitor. Also, this event
visitor can be combined with other event visitors using
std::pair to form an EventVisitorList.